Is a person held accountable for having ill thoughts or oppressing others in his mind without verbalizing them, and how does one get rid of self-talk?

It is forbidden to entertain ill thoughts about a Muslim unless a suspicious sign appears from them. This is supported by the words of Allah Almighty: "O you who have believed, avoid much [negative] assumption. Indeed, some assumption is sin." (Quran 49:12), and the words of the Prophet, peace and blessings be upon him: "Beware of suspicion, for suspicion is the falsest of speech." The forbidden suspicion is that which settles in the heart. As for fleeting thoughts, there is no accountability for them. If the forbidden ill suspicion occurs, repentance is obligatory.